Two-stage synthesis of



Reicsued Sept. 6, 1949 TWO-STAGE SYNTHESIS OF HYDROCABBONS Frank T.Barr, Summit, and Walter G. Sammann, Westfield,

Delaware Original No. 2,434,537,

Dec

Serial No. 568,514, cation for reissue 70,566

Our invention relates to the novel features hereinafter disclosed in thefollowing specification and claims, reference being had to theaccompanying drawing.

' The synthesis of hydrocarbons, including oils, from carbon monoxideand hydrogen is a matter of record. Our improvements involve a two-stageprocess in which we employ a fluid catalyst reactor in the first stagebed reactor in the second stage. Since the fluid catalyst type ofoperation is more flexible than the stationary bed type of process, weare enabled to secure the benefits of our invention which will bedescribed presently. We so control the process that in the first stageof our process, only those hydrocarbons which are gaseous or exist asvapors under the conditions of operation are formed in the first stageof our process. The reason underlying this technique is that we desireto avoidwax or liquid formation on the powdered catalyst employed in thefiuid" stage of the process. As is known, wax is formed in the normalsynthesis and this wax deposits on the catalyst requiring washing toremove the same. It is difficult to remove wax from a powdered catalyst.But more important perhaps,- is the fact that it is difficult to carryout a fluid catalyst type of operation in the presence of a liquid andhence we operate the process so as to limit the operation to theformation of hydrocarbons which are vaporized at operatingtemperaturesand then discharge the products of this first stage into asecond, fixed bed stage where the conversion is continued.

It is one of the objects of this invention, therefore, to conduct thesynthesis of hydrocarbons from C and hydrogen in a process whereadvantage is taken in both the fixed or stationary bed type of operationand the fluid catalyst type of operation, 1, e., in which the catalystis suspended in'the reaction gases. Another object of our presentinvention is to provide means for effecting the synthesis ofhydrocarbons, including normally liquid hydrocarbons, by reactingtogether CO and hydrogen in the presence of a suitable catalyst so as toproduce maximum quantities of desired hydrocarbons in an expeditious andrelatively cheap manner.

A further object of our invention is to provide means for synthesizingnormally liquid hydrocarbon oils by reacting CO and hydrogen in thepresence of a catalyst under conditions aflording rigid temperaturecontrol.

Other and further objects 0!. the inventlonwlll 55 a fluid catalystreactor N. J., assignors to Standard Oil Development Company, acorporation 01 dated January 13,1948,

and a fixed or stationary ordinary means of temperaturecontrol.

ember 16, 1944. January 12, 1949, Serial No.

carbons higher than methane.

Appli- 13 Claims. (Cl. 260-4495) 2 appear from the'iollowing moredetailed description and claims.

In the accompanying drawing, we have shown diagrammatically acombination of apparatus elements in which a preferred modification ofour invention may be carried into practical effect. Explaining at first,in a general way, the flow of reactants through the system illustratedin the accompanying drawing, we wish to point out the theory upon whichour improvements are based. In the synthesis of hydrocarbons from carbonmonoxide and hydrogen over stationary catalyst, the reaction in theinlet at rates suificiently high so that temperature control isdiflicult and expensive equipment is necessary to prevent temperaturerunaway from occurring. At the end of the reaction, however, thedecrease of concentration of reactants together with higher thermalstabilizing effect of the inerts makes the fixed bed operation moreamenable to Fluid catalyst operation for hydrocarbon synthesis, on theother hand, provides a means of temperature control suflicient toprevent runaway operation at any reactant concentration, but formationof liquid sometimes tends to coat the catalytic particles and reducetheir activity. Inasmuch as the fluid catalyst technique does not lenditself readily and economically to the removal of the liquid materialfrom the catalyst, such formation is distinctly disadvantageous.

As indicated we have found that it is advantageous to combine the twotypes of operation. The fluid catalyst operation is used on the freshsynthesis gas under conditions such that only a portion of the synthesisgas is converted to hydro- Conversion is limited so that materialsliquid under the conditions of operation are not formed. The tail gasfrom this stage is led to fixed catalyst synthesis reactors. Theconcentration of reactants is now suiliciently low that satisfactorytemperature control in fixed bed operation is obtained as describedabove and liquid products such as may be formed drain from the catalystwithout impeding theprogress of the reaction. The tail gas from thesecond stage is led to a cooler-condenser and naphtha recovery plant.Tail gas from the fluid catalyst section may be cooled if desired butoperation taking the gas directly from the separating system is simplerand ordinarily superior.

In the drawing similar reference characters refer to similar parts.

. Referring in detail to the drawing, i represents and 2 and 2Mrepresent section tends to proceed threere'actors of which sans 2!!indicates the internal structure and shows the reactor to contain tubest terminating in tube sheets .5, the catalyst being disposed in thetubes and for circulating a cooling medium from pipes 4 through theseveral reactors in parallel and withdrawing the cooling medium throughpipes 5. In the drawing the cooling medium is indicated as water. butobviously anycooling mediummay be used such, as molten salts, mercury,etc.

The drawing has been provided with suflicient legends and arrows toenable ease in reading and mere inspection is nearly suflicient tounderstand the operation thereof.

The synthesis gas enters the system proportioned in the ratio of about 2mols of H: per mol oi-.C0, and then is discharged into the bottom orfluid" reactor I where it passes upwardly in contact with powderedcobalt catalyst containing thoria or magnesia and supported on carrierssuch as silica gel or kieselguhr. This catalyst is known to the art.Other catalysts known to the art, such as iron promoted by alkali, mayalso be used. Proportion of H: to CO in the synthesis gas may not be thesame as required for cobalt catalysts, and is preferably adjusted to theoptimum, which for iron catalysts'is about 1:1. The catalyst sizeaverages 200 mesh, although it may vary from 100 to 400 mesh, As amatter or fact, a substantial portion say 20% or the catalyst may have asize of low than 20 microns. Depending on the size of the particles 01'catalyst, the velocity of the gases in reactor l is controlled withinthe limits of 0.25 to 5 feet per second preferably from V to 3 feet persecond. There results a fluid mass, i. e., a dense suspension ofcatalyst in gas. Also depending on the weight or amount of catalyst inthe reactor, there will be an upper dense phase level at L and above L,adlsengaging space S where the concentration 01 catalyst drops sharplyso that when the gas enters the solid-gas separating device(s) I (whichmay be one or more" "cyclone separators) the concentration oi. catalystis low (ranging from 0.075 to 0.003 lb. per cubic foot) As indicatedthegas passes through the separatofls) 1 wherein is removed and finallyexits via line 6. Separated catalyst is returned from the separator(s) 3via dip pipe I. 1

Since the reaction between CO and H2 is exothermic, it is advisable themanifolds M: and pipe I. Very accurate and rigid temperature control maybe achieved by the method indicated due to the turbulent state of thefluidized catalyst constantly particles or a gas, thus provision beingmade 0 additional catalyst The scrubbed vapors leave scrubber ll vialine It, then are forcedthrough a cooler ll, thence pass into aseparator Ila and thence pass to the stationary catalyst via line II. Inseparator lIa,

' water and hydrocarbons (boiling below about 400 F.) collect at thebottom or the separator and may be recovered therefrom.

As indicated, the

the bottom by operation 'of product is cooled in i1 and colsuits First,in reactor 1 Preferred Range Broad Range Cobalt Iron Catalysts CatalystsPressure in lbs. per sq. in..- mos-360 15-125 40-250 Temperature in (1cos l 850-700 400- 600-050 Through ut (cubi i eet CO 500 at 60 and iatmos. per

lb. of catalyst) hour)? l-15 1-15 V onversion 0 .per can 6 35-00 35-00Catalyst In powder form Second, in reactor z on original gss) .peroent-. 70-100 -100 80-100 Catalyst In the tom of pill; pellets,granules,

It is not necessary that the same composition of catalyst be used in theabove two stages.

ereas conditions of operation operation, cooperating in conjunction witheach other We have found that the combination of the two methods ofoplexiting is advantageous for the reasons set forth In fixed catalystoperation for the synthesis of hydrocarbons from carbon monoxide andhydroen. it has been ioundthat reaction rates near the entrance of inertmaterials builds u tion rates are slower to:- given exigencies oitemperam lince it is ordinarily necessary to adiust conditions to thoserequired at the point of maximum reaction rate, operation of theremaining catalyst volume is sometimes at conditions far removed fromoptimum eillciency. We avoid this diillculty by using the field catalysttechnique for operation on fresh synthesis gas, whence the criticalinitial conditions are better controlled, and the fixed catalystreactors operate at conditions nearing optimum efficiency for all partsof the bed.

In the use of the fluid catalyst technique for synthesis of hydrocarbonsfrom carbon monoxide and hydrogen another desirable process involves thepassage of the synthesis gas with catalyst suspended therein throughtubes whose walls act as heat transfer surface for removal of the heatof reaction. Optimum operating conditions are such that tubes of 3-4"inside diameter are used and the total passage length. is of the orderof 400-1000 ft. Variation of capacity of the reactor is achieved byputting two or more of these elements in parallel. The relationsindicated are based on obtaining optimum heat transfer rate togetherwith the desired time of contact for the reaction.

Here, however, the same difficulty arises as when the synthesis iscarried out using fixed catalyst as described above. Although variousmethods for obtaining control suited specifically to the reaction goingon in that part of the equipment under consideration have been proposed,we have found that a particularly advantageous method of obtaining saidcontrol involves the charging to the fresh synthesis gas of relativelysmall quantitles of fluid catalyst, such as will promote the reactiononly to a limited degree. Because of the high reactant concentration atthis point, reac tion rate can be maintained at a reasonable level witha smaller proportion of catalyst than at subsequent. points in thereaction path. At the point where reaction with the amount of catalystoriginally supplied has decreased to an undesirably low level,additional catalyst is supplied. The increased quantity of catalystbrings the reaction rate to the desired level. The charging ofadditional catalyst may be repeated a number of times as desired andconditions may be set so as to achieve high conversion of the reactingmaterials.

Construction of equipment having such relatively long passage lengthwould normally entail the assembly in series of a number of units ofshorter passage length. Thus, a passage length of 560 ft. is in one caseachieved by putting in series 28 units, each having tubes 20 ft. inlength. Transfer of the reacting materials, from one unit to another inthis arrangement is disadvantageous, however, owing to the necessity formaking the transfer tlmeas shcrtas possible, because of the absence ofadequate cooling surface. Although satisfactorily short transfer timecan be provided, velocities through the transfer lines are great andpressure drops are thereby large.

We have found that for fluid catalyst operation the employment of alarge number of passes within one shell is more satisfactory and isfeasible from a mechanical point of view. Whereas in fixed catalystoperation the use of several passes in one shell involves the necessityfor providing means for removal of the return bends for charging anddischarging catalyst, such arrangement is not required with fluidcatalyst. It is therefore possible to assemble with welded or otherwisepermanently secured return bends a large number of relatively shortlengths of tubing in a single of travel. For example, the 560 ft. oftravel referred to above may be achieved by inserting in one shell 28lengths of 20 ft. tubing connected in series by return bends. The returnbends as well as the tubes may be surrounded by the coolin medium whichin tumis and is outside the tubes. Fixed connection with lines outsidethe shell is necessary only at the chanical allowance to take care ofdifferential thermal expansion difllculties is not required. In

case it is desired to assemble a number of the multiple pass units inparallel in a single shell, inlet and outlet headers within the shellmay be provided. It is again necessary to provide secure connection tothe shell for only one inlet and one outlet pipe. This arrangement hasthe further advantage of making assembly and dismantling of theequipment simple, inasmuch as the entire tube bundle can be removed fromthe shell by breaking piping connections at only two points.

It is apparent that any combination of theseries and parallelarrangement within one shell may be made. Under certain conditionsachievement of the 560 ft. passage may be obtained, for instance, byconnecting '1 lengths of 20 ft. tubin in series in a. single shell andputting 4 such shells in series. The number of 20 ft. passes in eachshell need not be the same but may be varied as desired, providing onlythat the required total passage length be obtained.

It is pointed out that more than one fluid or fixed bed may be employedin the combination of fluid and stationary catalyst operation disclosedherein, and temperature control provided for each bed. For the fixed bedoperation, a suitable arrangement involves the assembling in a verticaltower of a plurality of thin beds of catalysts, the catalyst in allcases being disposed suitably close to aheat removal surface. forinstance, in small tubes or annular elements, and suitable separatorsbeing inserted in the shell on the cooling medium side to make possibleindependent control of the cooling medium temperature at each level.Catalyst tubes may extend through several cooling sections if desiredand would be limited only by the length of tube available. An alternatearrangement involves the use of short tubes, the length of each coolingsection, but with succeeding sections superimposed so closely that aminimum of free space between catalyst sections is allowed. Thisarrangement has the ad- 55 vantage that sections are transferable andindividually removed for maintenance. A crane may be provided forassembling and dismantling sections stacked as many on one another as isdesired.

It will be understood that periodically it may be necessaryto remove waxfrom the stationary beds of catalyst, for the said wax deposits on thecatalyst and diminishes its activity. The cata- 'lyst may be washed witha hydrocarbon oil, dur- 65 ing a shut down period toeiIect this result.The

details of washing the catalyst to de-wax the same are known to theprior art.

Numerous modifications of our'invention will appear to those familiarwith this art without 70 departing from the spirit thereof.

What we claim is: 1. In the process of synthesizing hydrocarbons.including hydrocarbon oils, by contacting carbon monoxide and hydrogenproperly stoichiometri- 75 cally proportioned at elevated temperaturesand 6 shell so as to obtain the desired length contained in the shellentrance and exit of the 28tube element. Mei can pressures with acatalyst, the improvement which comprises efl'ecting rigid temperaturecontrol by first suspending catalyst in the synthesis gases to form adense suspension, maintaining said suspension at conversion temperatureand under conversion pressure and limiting the time of contact or saidgases with said catalyst in said suspension so that hydrocarbons whichare liquid'at the operating conditions are not formedin sub-- stantialamounts while efiecting a substantial conversion of said carbon monoxideto hydrocarbans but not more than about 60% of the amount possible underthe reaction conditions, withdrawing residualsynthesis gases from saidsuspension and discharging them into a zone containing at leastonestationary bed of catalyst maintained-at reaction temperature and underreaction pressure, holding said synthesis gases in contact with 500". F.and the pressure from about to 250 lbs. per sq. in. gauge. a

5. The method of claim 1 in which the tem- V perature in the first stageis from about 375 to said stationary bed of catalyst for a sufficientperiod of time to convert additional amounts of carbon monoxide intonormally'liquid products and recovering said normally liquid productsfrom the second reaction zone.-

2. The method of synthesizing hydrocarbon oils which comprises forcing amixture of carbon monoxide and hydrogen into a first reaction zonemaintained under reaction conditions and containing a body of powderedcatalyst inthe form of a dense suspension, limiting contact; time ofreaction material with catalyst and temperature in said first reactionzone to suppress substantial formation of hydrocarbons which are liquidat the operating temperature while effecting substantial conversion ofsaid carbon monoxide to hydrocarbons but not more than about 60% of theamount possible under the reaction conditions, withdrawing gaseousreaction material from said first reaction zone and discharging it intoa zone containing at least one bed of stationary catalyst maintainedunder reaction conditions, carrying the reaction in said second reactionzone to maximum production of normallyliquid products and recoveringfrom said second zone a tainlng gasoline and gas oil.

3.-The method of claim 1 in which the temperature in the first stage isfrom about 350 to 500 F. and the pressure is from about 10 to 250 lbs.per sq. in. gauge.

4. The method of claim 2 in which the temproduct conperature in thefirst stage is from about 350 to 450 F. and the pressure from about 25to lbs. per sq. in. gauge.

6. The method of claim 2 in which the temperature in the first stage isfrom about 375 to 450 F. and the pressure from about 25 to 100 lbs. persq.'in. gauge.

7. The process specified in claim 1 in which the feed rate in the firststage is from about 1 to 15 cubic feet of CO per hour per lb. ofcatalyst.

The method specified in claim 2 in which the feed rate in the firststage is from about 1 to 15 cubic feet of CO per hour per lb. ofcatalyst.

9. The method of claim '1 in which the feed rate to the second stage isfrom 100 to 1000 volumes of gas per volume of catalyst per hour.

10. A method for synthesizing hydrocarbons which comprises forcing COand H2 through a fiuid mass of powdered cobalt containing catalyst in afirst reaction zone at temperatures within the range of from about 350to 500 F. at feed rates of 1 to 15 cubic feet of CO per hour per lb. ofcatalyst whereby the formation of hydrocarbon liquid at operatingconditions is suppressed, withdrawing the reactants and forcing themthrough at least one body of pilled catalyst in the form of a fixed bedin a second reaction zone at temperatures within the range of from about350 to 500 F. at feed rates of from about 100 to 1000 volumes of gas pervolume of catalyst per hour, causing a heat absorbing fluid to circulatein heat exchanging in relationship with the reactants in both zones andrecovering hydrocarbons including gasoline and gas oil from said secondzone.

11. The method of claim 10 including th step of cooling reactants duringtheir passage from the first to the second zone.

12. The method of claim 10 in which the feed to the first zone contains2 mols of H2 per mol No references cited.

